1. Field of the Invention
The invention relates to a damascene gate process, and more particularly to a process of forming damascene gates with a line width of 0.11 μm.
2. Description of the Related Art
As semiconductor manufacturing techniques have advanced, MOS gate length has scaled down to 100 nm, and the gate oxide layer is less than 3 nm thick. The conventional method of fabricating a gate is described in following. Shallow trench isolations (STI) are formed by SiO2 in the silicon substrate to define an active area. A gate oxide layer and a poly layer are sequentially formed and planarized. A mask layer is formed to cover the poly layer. The poly layer is defined as a poly gate by photolithography and etching. The substrate is implanted to form a lightly doped drain (LDD), and spacers are then formed.
Deposition, photolithography, and etching are performed repeatedly in the conventional process, thus fabrication costs cannot be reduced. When the polysilicon layer and the oxide layer with the exception of the active area are removed, the oxide layer is easily over-etched, damaging the silicon substrate under the oxide layer, thus other layers formed there on are not uniform. If the polysilicon layer and the oxide layer with the exception of the active area are not completely removed, stringers remain between gates or the gate and the bit line, thus short circuits occur in the gates.